1) Field of the Invention
This invention relates generally to a structure and a method of fabrication of a cooling device for a semiconductor device and more particularly to a Peltier Thermoelectric cooler that is formed on the backside of a semiconductor wafer.
2) Description of the Prior Art
The present invention relates to thermoelectric coolers (TEC's). It is known to use a thermoelectric cooler to lower the-operating-temperature of a semiconductor device such as a laser. A thermoelectric cooler includes a plurality of thermoelectric cooling elements, which are constructed of materials with dissimilar characteristics. The elements are connected electrically in series and thermally in parallel to provide a plurality of thermoelectric couples. Each thermoelectric couple includes one element having a first characteristic and another element having a second characteristic. The thermoelectric couples are connected between two plates which function as a hot side and a cold side of a thermoelectric cooler. The hot side is thermally connected to a heat sink and the cold side is thermally connected to the semiconductor device.
Thermoelectric cooling is achieved by passing a DC electric current through the thermoelectric cooler. Thermal energy is drawn from the cold side to the hot side at a rate which is proportional to current passing through the circuit and the number of couples. At the hot side, the thermal energy is dissipated by the heat sink. The thermoelectric cooling effect is greatly increased when the dissimilar conducting materials used are semiconducting materials.
The dissimilar semiconducting materials generally used for thermoelectric cooling are N-type material (more electrons than necessary to complete a Perfect molecular lattice structure) and P-type material (fewer electrons than necessary to complete a perfect molecular lattice structure, thus providing holes). The extra electrons in the N-type material and the holes in the P-type material are called "carriers" which function to above the thermal energy from the cold side to the hot side.
Conventionally, TE coolers have been formed separately from the integrated circuit device. However, there is a need to develop an TE device that has increased cooling capability and is smaller.
The importance developing TE coolers for semiconductor devices is evidenced by the extensive technological development directed to the subject, as documented by the relevant patent and technical literature. The closest and apparently more relevant technical developments in the patent literature can be gleaned by considering U.S. Pat. No. 4,238,759 (Hunsperger) which shows a Peltier device that cools an adjacent P-N junction. The TE cooler is to be mounted on the front side (e.g., device side) the chip. U.S. Pat. No. 4,279,292 (Swiatosz) shows a TE cooler in contact with a central area of integrated circuit. U.S. Pat. No. 5,012,325 (Mansuria et al.) shows a TE IC package. U.S. Pat. No. 5,362,983 (Yamamura et al.) shows a TE module with a series connection. U.S. Pat. No. 5,419,780 (Suski) shows a Thermoelectric cooler contacting an IC and connected to a fan for additional cooling. U.S. Pat. No. 5,285,108 (Hasteing et al.) shows a Thermoelectric (TE) cooler contacting an integrated circuit (IC).